In reciprocating internal combustion engines, a piston is guided for longitudinal movement in a cylinder and the piston drives a crankshaft via a connecting rod. The crankshaft is rotatably journalled in a crankcase which contains lubricating oil for the crank drive. The connecting rod is pivotally held on a crankpin arranged eccentrically to the rotational axis of the crankshaft.
If such a reciprocating engine is utilized in a portable handheld work apparatus such as a motor-driven chain saw or the like to drive the work tool, then the engine is regularly moved out of its stand up normal alignment when, for example, the work tool and therefore the drive motor are guided sideways or even overhead. Without suitable countermeasures, the lubricating oil flows in the direction of the piston and can enter the combustion chamber. This can effect the proper operation of the engine especially when the apparatus is put down at engine standstill in the overhead position of the engine. It is even possible that lubricating oil drips out of the engine.
German patent publication 197 38 155 discloses a four-stroke internal combustion engine having a chamber next to the cylinder and which chamber contains lubricating oil. The chamber is configured as an oil receptacle with baffle walls within the crankcase in which the lubricating oil is taken up when the cylinder is in an overhead position. An oil catcher is movable with the crankpin about the rotational axis of the crankshaft and projects into the chamber containing the lubricating oil. The oil catcher is intended to catch lubricating oil and spray the lubricating oil onto the components to be lubricated at high rpm of the crankshaft.
In the known engine, the crankcase is configured to have a double wall. The inner baffle wall encloses the components of the crank drive and the outer wall of the crankcase surrounds the inner wall. The space, which is formed between the baffle wall and the outer wall, holds the lubricating oil for the crank drive. A slot is formed in the baffle wall and extends on the side of the baffle wall in the peripheral direction. This side of the baffle wall lies opposite the piston. The oil catcher projects through the slot into the chamber containing the lubricating oil and the oil bath contained therein.
The outer wall of the lubricating oil chamber is connected to the inner wall above the crankshaft, that is, on the side facing toward the cylinder whereby an oil catch is formed. In the side position and in the overhead position, the oil catch holds the lubricating oil, which flows in the direction of the cylinder, back into the oil chamber. The crank chamber, which is closed off by the baffle wall, is thereby separated from the lubricating oil chamber whereby a wetting of the backside of the piston is precluded in a position of the engine deviating from the normal alignment. The oil catcher is configured radially on the crankpin but enters only segmentwise through the slot into the oil chamber during its revolution and therefore can only catch lubricating oil and move the same to the crank drive when the engine is in its upright position and the lubricating oil is disposed at the base of the lubricating chamber and accessible for the oil catcher. Although the oil is prevented from entering into the crank chamber in the overhead position of the engine, a lubrication is, however, no longer provided so that operating disturbances of the engine can occur very quickly.